Answer to Parasite Case of the Week 529: Pollen grains
Congratulations to everyone who wrote in with the correct answer. Most of you recognized this as some type of artifact, with only a few suggesting that these might be helminth eggs. As Old One mentioned, "These structures superficially resemble ascarid eggs. Size, and surface texture would help with differentiation. Toxocara canis is 80-85 micrometers in greatest dimension with a golfball pitted surface texture. T. cat is 65-70 micrometers it also has the golfball pitting but smaller and less distinct then that of T. canis. Baylisascaris procyonis is 63-88 u and has a granular surface texture. I will always checkout surface texture by focusing up and down on the focal plane of an eggs surface. It is surprising the things you'll see. This is how we diagnosed a mixed infection of T. canis and B. procyonis in a dog." (!)
Here is a side-by-side comparison of the pollen in our case and a Toxocara sp. egg. Note also the pores which help to differentiate the pollen grain from a true helminth egg.
I didn't provide a size of the pollen in this case, but estimate the grains to be ~40 micrometers long.
Interestingly, Old one and SilvaB suggested that these might be pollen of the cornflower (Psephellus). I don't know much about pollen, but a quick google search revealed THIS manuscript which has some nice photos of several pollen genera that bear a resemblance to the pollen in this case. Enjoy!